This invention relates to the field of optoelectronics and, more specifically, to polarization controllers.
Light is an electromagnetic wave composed of electric and magnetic fields. The orientation of these fields defines the light""s polarization. As light propagates through an optical fiber, variables such as temperature and stress can cause random and arbitrary changes in the state of the light""s polarization, reducing the distance that the light travels due to signal degradation. These changes in the state of polarization can cause problems in fiber optic applications such as optical communication systems and sensors. Polarization controllers can reduce signal degradation in optical systems by converting any incoming polarization state back to the intended polarization state during optical transmissions. The principle of the polarization controller is that a desired polarization state is obtained by using appropriate phase retarders or phase shifters which can transform a state of polarization (SOP) to another arbitrary SOP. For the purposes of achieving this result, two design aspects of polarization controllers are generally considered critical. First, the controller must be able to convert an arbitrary, time variant state of polarization into a specific, desired polarization state. Second, the polarization controller must be able to convert the state of polarization for a wide range of wavelengths for use in optical communication systems, such as those utilizing wavelength division multiplexing (WDM).
Previous work in the field has proposed several different concepts for polarization controllers possessing the two desired design aspects described above, based on mechanically tunable as well as electro-optic effects. For example, see R. Noe, H. Heidrich, D. Hoffman, xe2x80x9cEndless Polarization Control Systems for Coherent Optics,xe2x80x9d Journal of Lightwave Technology, pp. 1199-1207, 1988. It seems that presently, the straight-forward solution for achieving a polarization controller with the ability to convert the state of polarization for a wide range of wavelengths consists of an optical demultiplexer, single channel polarization controllers, and an optical multiplexer. This hybrid combination however, can be costly and physically occupies a large form factor.
The invention comprises a method and apparatus for providing integrated broadband polarization control. The invention enables an integrated polarization controller, suitable for realization on low-cost material in planar waveguide technology, and compact in size, which can transform a SOP to another arbitrary SOP for a wide range of wavelengths for use in optical communication systems, such as those utilizing wavelength division multiplexing (WDM).
A method for providing broadband polarization control according to an embodiment of the invention includes the steps of splitting an optical signal into a first polarization component and a second polarization component, the second polarization component orthogonal to the first polarization component, retarding the phase of the first polarization component, and recombining the first polarization component and the second polarization component. Alternatively, the method can further include the steps of converting the first polarization component into the orthogonal polarization prior to the retarding, such that the first polarization component and the second polarization component propagate with the same polarization, and converting the first polarization component back to its original polarization state prior to recombining it with the second polarization component.
An apparatus for providing integrated broadband polarization control according to another embodiment of the invention includes a splitting optic for splitting received optical signals into a first polarization component and a second polarization component, the second polarization component orthogonal to the first polarization component, and the first and second polarization components propagating through separate branches of the broadband polarization controller, at least one wavelength selectable phase shifter, for retarding the phase of the first polarization component, and a combining optic for combining the first polarization component and the second polarization component.